IL SOTTOSUOLO DEL CASTRUM DI GRADO (ADRIATICO SETTENTRIONALE): STUDI PRELIMINARI PER UNA RICOSTRUZIONE PALEOGEOGRAFICA

Abstract

Marocco R., Maselli Scotti F., Melis R. & Vio E., The subsoil of the castrum of Grado (Northern Adriatic Sea): a preliminary palaegeographic reconstruction. (IT ISSN 0394-3356, 2005).
A 12 m deep exploration well drilled on the church-square of the Palaeochristian Basilica of Santa Maria delle Grazie in Grado allowed
a reconstruction of the palaeogeographic evolution of the barrier island. The results indicate that the castrum of the island of Grado
was built around 4th Century AD on the ridge of a prograding delta lobe of a river with intense solid transport. The litho-biostratigraphic analysis of the subsoil testifies to the presence of paralic deposits at the bottom of the well, which gradually pass to muddy sands of fully circumlittoral environment, and back to the original paralic environment. The sequence, in fact, represents a micro transgressiveregressive hemicycle entirely developed in a marine environment and has corresponding events only in the subsoil of the current Tagliamento River delta. Ceramic fragments recovered from -1,6 m to -3,6 m depth and from -4,6 to -6,2 m depth allow us to suppose the existence of a port or other human coastal activities (villas?) dating back, at least in the top interval, to the 1st Century BC - 1st Century AD, soon after the foundation of the Roman colony of Aquileia (181 BC). The second interval with archaeological remains, which was discovered also in another well very close to the investigated one, let us believe that the area of Grado was settled well prior to the famous Roman colony foundation, due to its proximity to the outlet of a navigable river (palaeo Isonzo ?).
The results obtained from our data highlight a slightly different coastal evolution of the littoral area of Veneto and Friuli Venezia Giulia,
already described by R. Marocco (1991), and testify to the importance of ancient river diversions in reconstructing palaeocoastlines of
northeastern Adriatic Sea.